Oscillator having multiple oscillation units

ABSTRACT

The present invention is an oscillator including: first transistors outputting oscillation signals of different oscillation frequencies to collectors; a common node to which outputs of emitters of the first transistors are connected and input; a feedback circuit feeding an output of the common node to bases of the first transistors; and isolation circuits that are respectively provided between the emitters of the first transistors and the common node and cut off high frequency components from the common node.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to oscillators, and moreparticularly, to an oscillator having multiple oscillation units capableof outputting different oscillation frequencies.

2. Description of the Related Art

Oscillators, particularly, voltage-controlled oscillators have been usedin mobile communication equipment such as PHS (Personal HandyphoneSystem), wireless LAN (Local Area Network), and transceivers.

There is an oscillator capable of oscillating at selectable differentfrequencies. For example, Japanese Patent Application Publication No.2004-64567 discloses an oscillator that oscillates at a selected one ofthree oscillation frequencies. The oscillators are required to haveimproved C/N (Carrier to Noise) ratios. Further, the oscillator capableof oscillating at selectable oscillation frequencies is required to havea downsized circuitry.

SUMMARY OF THE INVENTION

An object of the present invention is to improve the C/N ratio anddownsize the circuitry. According to an aspect of the present invention,there is provided an oscillator including: first transistors outputtingoscillation signals of different oscillation frequencies to collectors;a common node to which outputs of emitters of the first transistors areconnected and input; a feedback circuit feeding an output of the commonnode to bases of the first transistors; and isolation circuits that arerespectively provided between the emitters of the first transistors andthe common node and cut off high frequency components from the commonnode. The feedback circuit that feeds the outputs of the emitters of thefirst transistors to the bases can improve the C/N ratio. The downsizingcan be achieved by the arrangement of connecting the emitters of thefirst transistors to the common node via the respective isolationcircuits. Further, the isolation circuits can prevent signals fromflowing back to the emitters of the first transistors. According toanother aspect of the present invention, there is provided an oscillatorincluding: oscillation units outputting oscillation signals of differentoscillation frequencies; a common node to which other output signals ofthe oscillation units are connected and input; a feedback circuitfeeding an output of the common node to the oscillation units; andisolation circuits that are respectively provided between the otheroutput signals of the oscillation units and the common node and cut offhigh frequency components from the common node. The feedback circuitthat feeds the other output signals of the oscillation units improvesthe C/N ratio. Downsizing can be achieved by using the common node towhich the oscillation units are connected. The isolation circuitsprevent signals from flowing back to the oscillation units.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the present invention will be described indetail with reference to the 30 following drawings, wherein:

FIG. 1 is a block diagram of an oscillator in accordance with a firstembodiment;

FIG. 2 is a circuit diagram (part 1) of an oscillator in accordance withthe first embodiment; and

FIG. 3 is a circuit diagram (part 2) of an oscillator in accordance withthe first embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A description will now be given, with reference to the accompanyingdrawings, of exemplary embodiments of the present invention.

First Embodiment

FIG. 1 is a block diagram of an oscillator in accordance with a firstembodiment. Referring to FIG. 1, the oscillator includes oscillationunits 101 through 10 n, a feedback circuit 40 and a second switchcircuit 50. The oscillation units 101 through 10 n respectively includefirst switch circuits 31 through 3 n, oscillation circuits 21 through 2n, and isolation circuits 61 through 6 n. The first switch circuits 31through 3 n turn ON and OFF power supplies to the oscillation units 101through 10 n. The oscillation circuits 21 through 2 n output oscillationsignals of mutually different frequencies to output terminals Tout1through Toutn, respectively. The isolation circuits 61 through 6 nrestrict high-frequency noise from a common node N1 to the oscillationcircuits 21 through 2 n. The oscillation circuits 21 through 2 n areconnected to the common node N1 via the isolation circuits 61 through 6n. The common node N1 is input to the feedback circuit 40, and theoutput of the feedback circuit 40 is connected to a feedback node N2.The feedback node N2 is input the oscillation circuits 21 through 2 nvia the first switch circuits 31 through 3 n, respectively. The feedbacknode N2 is connected to a power supply terminal Tb via the second switchcircuit 50.

FIGS. 2 and 3 are respectively circuit diagrams of the oscillator of thefirst embodiment. Parts (A) and (B) of FIG. 2 are respectively connectedto parts (A) and (B) of FIG. 3. The oscillation units 101, 102 through10 n are the same as each other, and therefore, only the oscillationunit 10 n will now be described, while a description of the otheroscillation units 101 and 102 will be omitted. The oscillation unit 10 nmainly includes a resonance circuit 1 n, the oscillation circuit 2 n,the first switch circuit 3 n and a second inductor L3 n, which is theisolation circuit.

The resonance circuit 1 n includes variable capacitance diodes D1 n andD2 n, capacitors C41 n and C42 n, and inductors L41 n and L42 n. Thecathodes of the variable capacitance diodes D1 n and D2 n are coupled toa control terminal Ta via the choke inductor L1 n. The 10 controlterminal Ta is grounded via a capacitor C5 for removal of high frequencycomponents. The anode of the variable capacitance diode D1 n is groundedvia the capacitor C41 n and the inductor L41 n connected in parallel.Similarly, the anode of the variable capacitance diode D2 n is groundedvia the capacitor C42 n and the inductor L42 n connected in parallel. Avoltage applied to the control terminal Ta changes the capacitancevalues of the variable capacitance diodes D1 n and D2 n. Thus, theresonance circuit in resonates at a desired resonant frequency.

The oscillation circuit 2 n includes a first transistor Q1 n, which isan NPN bipolar transistor, capacitors C1 n and C2 n, and a resistor R3n. The base of the first transistor Q1 n is grounded via the capacitorC1 n and C2 n connected in series. A node between the capacitors C1 nand C2 n is connected to the emitter of the first transistor Q1 n viathe resistor R3 n. A node N3 n is connected to the collector of thetransistor Q3 n of the switch circuit 3 n via a resistor R4 n. Theoscillation circuit 2 n forms a Clap oscillation circuit, which is akind of Colpitts oscillation circuit. The node N3 n is connected to theanodes of the variable capacitance diodes D1 n and D2 n of the resonancecircuit 2 n via coupling capacitors C31 n and C32 n. Thus, theoscillation circuit 2 n oscillates at the resonance frequency of theresonance circuit in, and the oscillation signal is output via thecollector of the first transistor Q1 n. The resistor R3 n restrictsabnormal oscillation of the oscillation circuit 2 n. The oscillationsignal output via the collector of the first transistor Q1 n is outputvia the output terminal Toutn having an impedance matched with theoutput impedance. The capacitor C12 n shuts off the dc component. Thecollector of the first transistor Q1 n is supplied from the power supplyterminal Tb, with a dc voltage via a line S1 n (such as a strip line),which is a choke inductor.

The first switch circuit 3 n includes a PNP bipolar transistor Q3 n, andresistors R1 n and R2 n. The emitter of the transistor Q3 n is connectedto the power supply terminal Tb via a resistor R6 and the second switchcircuit 50. A switch terminal Tswn is connected to the base of thetransistor Q3 n via the resistor R2 n, and the resistor R1 n isconnected between the base and emitter of the transistor Q3 n. Thecollector of the transistor Q3 n is connected to the base of the firsttransistor Q1 n via the resistor R4 n. The resistor R2 n is used toprevent the first transistor Q1 n from being broken, and preferably hasa resistance in the range of a few kiloohms to tens of kiloohms. Theresistor R1 n is used to reliably turn OFF the first transistor Q1 n.

The first switch circuit 3 n supplies power to the oscillation circuit 2n in accordance with a signal applied to the switch terminal Tswn. Morespecifically, when the first switch circuit 3 n is turned ON, power issupplied to the oscillation circuit 2 n from the power supply terminalTb, and the oscillation unit 10 n supplies the oscillation signal to theoutput terminal Toutn. In contrast, when the first switch circuit 3 n isturned OFF, no power is supplied to the oscillation circuit 2 n, and theoscillation unit 10 n does not produce the oscillation signal.

The emitters of the first transistors Q11, Q12 through Q1 n of theoscillation circuits 21, 22 through 2 n are connected to the common nodeN1 via second inductors L31, L32 through L3 n, respectively. The commonnode N1 is grounded via a first resistor R5 and a first capacitor C7connected in parallel. The first resistor R5 is used to adjust currentcomsumed, and preferably has a resistance of tens of ohms. The firstcapacitor C7 is used to adjust the balance of the output level, andpreferably has a capacitance of a few pF. The common node N1 isconnected to the feedback circuit 40.

The feedback circuit 40 includes a second transistor Q2, which is an NPNbipolar transistor, a second resistor R90 and a second capacitor C9. Thebase of the second transistor Q2 is connected to the common node N1 viaa coupling capacitor C110. The coupling capacitor C110 is preferablyprovided to strengthen the coupling between the oscillation circuit 2 nand the feedback circuit 40 and prevent the signal from the firsttransistor Q1 n from being delayed. For example, the coupling capacitorC110 may have a capacitance value of hundreds of nF. The base of thesecond transistor Q2 is grounded via the second capacitor C9, which is afeedback capacitor. The emitter of the second transistor Q2 is grounded.The second resistor R90 is connected between the base and the collectorof the second transistor Q2. The second resistor R90 prevents thecollector current from flowing back to the base. The collector of thesecond transistor Q2 is connected to the feedback node N2 via a resistorR10. The resistor R10 is a bias resistor. The feedback node N2 isconnected to the first switch circuits 31 through 3 n of the oscillationunits 101 through 10 n. Thus, the signals of the emitters of the firsttransistors Q11 through Q1 n of the oscillation units 101 through 10 nare fed back to the bases of the first transistors Q11 through Q1 n viathe single common node N1 and the feedback circuit 40.

The feedback node N2 is connected to the power supply terminal Tb viathe resistor R6 and the second switch circuit 50. The second switchcircuit 50 includes a PNP bipolar transistor Q41, an NPN bipolartransistor Q42, and resistors R51 through R54. The second switch circuit50 connects and disconnects the power supply terminal Tb and thefeedback node N2 in accordance with a switch signal applied to a switchterminal SWen. When the second switch circuit 50 is turned OFF, powersupply from the feedback circuit 40 and the oscillation units 101through 10 n can be shut off. The capacitor C2 connected between thefeedback node N2 and the ground is for use in removal of high-frequencycomponents.

The oscillator of the first embodiment includes multiple firsttransistors Q11 through Q1 n in which different oscillation frequenciesare output via the collectors thereof. The emitter outputs of the firsttransistors Q11 through Q1 n are coupled via the respective isolationcircuits and are then connected to the common node N1. Further, theoscillation circuit is equipped with the feedback circuit 40 that feedsthe output of the common node N1 back to the bases of the firsttransistors Q11 through Q1 n. Furthermore, the oscillator has theinductors L31 through L3 n, which are the isolation circuits that areprovided between the emitters of the first transistors Q11 through Q1 nand the common node N1 and cut off the high-frequency components fromthe common node N1.

The first transistors Q11 through Q1 n are supplied with the resonancesignal via the bases, and the voltages of the emitters are followed bythe input sides. That is, the first transistors Q11 through Q1 n areconnected in the collector grounded formation (emitter follower). Thecollector-grounded circuit outputs, via the emitter, a waveform that isthe same waveform as that of the base voltage and is offset by −0.6 Vfrom the base voltage. Further, the collector-grounded circuit has ahigh input impedance (the impedance of the base), a low output impedance(the impedance of the emitter), and a voltage gain approximately equalto 1. Furthermore, the collector-grounded circuit has low distortion andgood frequency characteristics. Thus, the C/N ratio can be improved byfeeding the emitter outputs of the first transistors Q11 through Q1 n tothe bases of the first transistors Q11 through Q1 n via the feedbackcircuit 40.

The oscillation circuits 21 through 2 n may employ the first transistorsQ11 through Q1 n having a large current gain β, so that the basecurrents of the first transistors Q11 through Q1 n can be amplified toflow large currents through the collectors. It is thus possible toobtain the large oscillation signals via the output terminals Tout1through Toutn. As the oscillation signal has increased power, the C/Nratio can be enhanced.

As described above, the signals are fed back to the bases of the firsttransistors Q11 through Q1 n from the emitters thereof via the feedbackcircuit 40. The oscillation signals are output from the collectors ofthe first transistors Q11 through Q1 n. It is thus possible to improvethe C/N ratio and restrict phase noise.

The emitters of the first transistors Q11 through Q1 n of theoscillation units 101 through 10 n are connected to the common node N1,and are fed back to the bases of the first transistors Q11 through Q1 nby means of the single feedback circuit 40. It is thus possible tominiaturize the oscillator.

In the case where the emitters of the first transistors Q11 through Q1 nare commonly connected to the feedback circuit 40, unnecessary signalsmay flow back to, for example, the emitter of the first transistor Q11from the feedback circuit 40 and the other first transistors Q12 throughQ1 n. Particularly, unnecessary signals of frequencies higher than theoscillation frequency such as harmonic components may flow back. Withthe above in mind, in accordance with the first embodiment, the secondinductors L31 through L3 n serving as the isolation circuits areprovided between the emitters of the first transistors Q11 through Q1 nto the common node N1. It is thus possible to prevent the unnecessarysignals of frequencies higher than the oscillation frequency fromflowing back to the emitter of the first transistor Q11 from thefeedback circuit 40 and the other first transistors Q12 through Q1 n.

The first embodiment has the multiple first switch circuits 31 through 3n that turn ON and OFF the first transistors Q11 through Q1 n. Byoperating one of the oscillation units 101 through 10 n, the desiredoscillation frequency is available.

The first switch circuits 31 through 3 n are connected between the powersupply terminal Tb and the bases of the first transistors Q11 through Q1n. It is thus possible to selectively operate the oscillation units 101through 10 n. The first switch circuit 31 may be provided between thecollectors of the first transistors Q11 through Q1 n and the powersupply terminal Tb.

Preferably, the output of the feedback circuit 40 is coupled with thepower supply terminal Tb. It is thus possible to use the same line forpower supply and transmission of feedback signal to the feedback circuit40.

Preferably, the common node N1 is grounded via the first capacitor C7and the first resistor R5 connected in parallel. The first resistor R5may adjust the current consumed, and the first capacitor C7 adjusts thebalance of the output level.

Preferably, the feedback circuit 40 includes the second transistor Q2,and the common node N1 is connected to the base of the second transistorQ2. Further, the bases of the first transistors Q11 through Q1 n arecoupled with the collector of the second transistor Q2. Thus, thefeedback circuit 40 has the emitter-grounded circuitry. With thisstructure, the emitter outputs of the first transistors Q11 through Q1 nare fed back to the bases of the first transistors Q11 through Q1 n, andthe C/N ratio can be improved.

Preferably, the common node N1 is connected to the base of the secondtransistor Q2 via the coupling capacitor C110, and the base of thesecond transistor Q2 is grounded via the second capacitor C9. The secondresistor R90 is connected between the base and the collector of thesecond transistor Q2. The second capacitor C9 functions as a feedbackcapacitor. The second resistor R90 prevents reverse flow of thecollector current to the base.

Preferably, the second switch circuit 50 is provided between the powersupply terminal Tb and the feedback node N2 (that is, the firsttransistors Q11 through Q1 n). The second switch circuit 50 cuts off thepower supply to the oscillation units 101 through 10 n all at once.

The third capacitors C11 through C1 n and the fourth capacitors C21through C2 n respectively connected in series are provided between thebases of the first transistors Q11 through Q1 n and the ground. Thenodes N31 through N3 n between the third capacitors C11 through C1 n andthe fourth capacitors C21 through C2 n are connected to the emitters ofthe transistors Q11 through Q1 n, respectively. Thus, the oscillationcircuits 21 through 2 n have the configuration of the Clap oscillationcircuit including the coupling capacitors C311 through C31 n and C321through C32 n.

Preferably, the isolation circuits may include the second inductors L31through L3 n. It is thus possible to configure the simplified isolationcircuits capable of cutting off higher frequency components than theoscillation frequency.

In the first embodiment, the output terminals Tout1 through Toutn of theoscillation units 101 through 10 n are separately provided.Alternatively, a common output terminal may be employed.

In the first embodiment, the oscillation signals of the frequencies ofthe oscillation units 101 through 10 n are output via the collectors ofthe first transistors Q11 through Q1 n. The different outputs of theoscillation units 101 through 10 n applied to the common node are theemitter outputs of the first transistors Q11 through Q1 n. Further, theinputs of the oscillation units 101 through 10 n output by the feedbackcircuit 40 are the bases of the first transistors Q11 through Q1 n. Theoutputs and inputs of the oscillation units 101 through 10 n are notlimited to the above.

Although a few specific exemplary embodiments employed in the presentinvention have been shown and described, it would be appreciated bythose skilled in the art that changes may be made in these exemplaryembodiments without departing from the principles and sprits of theinvention, the scope of which is defined in the claims and theirequivalents.

1. An oscillator comprising: first transistors outputting oscillationsignals of different oscillation frequencies from collectors; a commonnode to which outputs of emitters of the first transistors are connectedand input; a feedback circuit feeding an output of the common node tobases of the first transistors; and isolation circuits that arerespectively provided between the emitters of the first transistors andthe common node and cut off high frequency components from the commonnode.
 2. The oscillator as claimed in claim 1, further comprising firstswitch circuits that respectively turn ON and OFF the first transistors.3. The oscillator as claimed in claim 2, wherein the first switchcircuits are respectively coupled between a power supply terminal andthe bases of the first transistors.
 4. The oscillator as claimed inclaim 1, wherein: the feedback circuit has a second transistor; and acollector of the second transistor is connected to a power supplyterminal.
 5. The oscillator as claimed in claim 1, wherein the commonnode is grounded via a first capacitor and a first resistor connected inparallel.
 6. The oscillator as claimed in claim 1, wherein the feedbackcircuit includes a second transistor, and the common node is connectedto the base of the second transistor, the bases of the first transistorsbeing connected to the collector of the second transistor.
 7. Theoscillator as claimed in claim 6, wherein; the common node is connectedto the base of the second transistor via a coupling capacitor; the baseof the second transistor is grounded via a second capacitor; and aresistor is connected between the base and collector of the secondtransistor.
 8. The oscillator as claimed in claim 1, further comprisinga second switch circuit between a power supply terminal and the firsttransistors.
 9. The oscillator as claimed in claim 1, further comprisingthird capacitors and fourth capacitors connected in series between thebases of the first transistors and ground; and nodes of the third andfourth capacitors are connected to the emitters of the firsttransistors.
 10. The oscillator as claimed in. claim 1, wherein theisolation circuits respectively include second inductors.